The present invention relates to a voltage supply circuit, more particularly relates to a voltage supply circuit capable of realizing low power consumption by supplying to a semiconductor integrated circuit a minimum operating power source voltage required for maintaining normal operation and a control method of the voltage.
The power consumption of a semiconductor integrated circuit depends on the supplied operating power source voltage. On the other hand, when the operating power source voltage falls, the operating speed of the semiconductor integrated circuit falls. Accordingly, it is necessary to supply to the semiconductor integrated circuit a minimum operating power source voltage by which the operating speed of the semiconductor integrated circuit satisfies a predetermined reference value.
Generally, as a means to realize lower power consumption of an LSI (large-scale semiconductor integrated circuit), the delay time of a critical path in the LSI is constantly monitored and the voltage supplied to the LSI is controlled so that the delay time of the critical path becomes shorter than a certain reference value. Due to this control, a minimum voltage enabling the LSI to maintain normal operation is supplied and a lower power consumption can be realized while maintaining normal operation of the LSI.
A voltage supply circuit for supplying such a power source voltage normally comprises a replica circuit for monitoring a delay time of a critical path of the semiconductor circuit, a delay detection circuit for detecting the delay time of the replica circuit, a voltage generation circuit, and a control circuit for controlling a generated voltage of the same. The voltage generated by the voltage generation circuit is supplied as an operating power source voltage to the semiconductor integrated circuit and the replica circuit, respectively. Normally, the replica circuit is designed to have about the same delay time as that of a critical path in the semiconductor integrated circuit. Also, it is designed to have a slightly longer delay time than that of the critical path considering an operating margin of the LSI in some cases.
As explained above, the operating speed of a semiconductor integrated circuit changes in accordance with the power source voltage supplied. For example, the operating speed is high when the supplied power source voltage is high and conversely, the operating speed becomes low when the supplied power source voltage is low. The replica circuit is supplied with the same operating power source voltage as that of the semiconductor integrated circuit and has almost the same delay time as that of the critical path of the semiconductor integrated circuit, so the higher the supplied power source voltage, the shorter the delay time, and conversely the lower the supplied power source voltage, the longer the delay time. Therefore, whether or not the operating speed of the semiconductor integrated circuit satisfies a predetermined reference value can be judged by detecting the delay time of the replica circuit.
The operating voltage supplied can be controlled by inputting a predetermined signal to the replica circuit and detecting a time delay of an output signal corresponding thereto. Here, as the input signal, for example a one shot pulse or a cyclic clock signal is input to the replica circuit. The delay time of the replica circuit can be detected in accordance with a time difference or a phase difference of an output signal of the replica circuit and the above input signal. Then, the detected delay time is compared with the predetermined reference value and the generated voltage of the voltage generation circuit is controlled in accordance with the result of the comparison. For example, when the delay time of the replica circuit is larger than the predetermined reference value, control is performed for raising an output voltage of the voltage generation circuit, while conversely, when the delay time of the replica circuit is smaller than or equal to the predetermined reference value, control is performed for lowering the output voltage of the voltage generation circuit.
As a result of the above control, the semiconductor integrated circuit is supplied with a minimum voltage for enabling normal operation and a lower power source consumption is attained.
In the above conventional voltage supply circuit explained above, however, when the delay time of the replica circuit detected by the delay detection circuit is larger than the predetermined reference value and the supplied voltage has to be raised, operating errors of the semiconductor integrated circuit may occur if the output from the voltage generation circuit, that is, the operating power source voltage, is not promptly raised. The delay time of the semiconductor integrated circuit and the replica circuit may become larger than the reference value when the circuit starts to operate or the load of the voltage generation circuit is abruptly increased. In this case, it is preferable that the supplied voltage of the voltage generation circuit be controlled to reach a desired voltage level in a short time to maintain the normal operation of the semiconductor integrated circuit.
In a conventional voltage supply circuit, however, there is a limit on the extent of control of the supplied voltage by the control circuit, so when it is necessary to quickly raise the supplied voltage, an operating delay arises and the operation of the semiconductor integrated circuit may become unstable for a certain time.
This will be explained in further detail with reference to FIG. 12 below.
For example, the control circuit detects that the delay time is larger than the reference value at a time A and requests the voltage generation circuit to raise the output voltage by a certain amount of increase. However, if the delay time is still larger than the predetermined reference value despite the amount of increase, the control circuit again requests the voltage generation circuit to raise the output voltage at a time B. By repeating the same, finally, the level of the supplied voltage is controlled to be high so that the delay time does not exceed the predetermined reference value, but there is a possibility that the semiconductor integrated circuit will not be able to normally operate during this time.
By controlling the amount of increase of the output voltage of the voltage generation circuit to be large, it is possible to deal with abrupt changes of the load etc. and possible to alleviate the above problem to some extent. However, when it is detected that the delay time of the semiconductor integrated circuit is lower than the predetermined reference value and the control circuit requests the voltage generation circuit to lower the output voltage, if the amount of reduction of the voltage is set to be large in the same way as the amount of increase, the operating voltage supplied abruptly falls and the semiconductor integrated circuit may become unable to normally operate. In this case, the control circuit may fall into an unstable condition of repeatedly requesting the voltage generation circuit to raise and reduce the amount of output voltage.
Also, in the above conventional voltage supply circuit, to make the characteristics of the replica circuit completely equivalent to those of the critical path inside the actual LSI, it is necessary that not only the number of gates of the critical path but also the interconnection capacitance and resistance of the critical path all be accurately imitated. This is difficult in practice. Therefore, the delay time detected by the replica circuit does not always accord with the delay time of the critical path of the actual LSI.
Here, as an example, the power source voltage-delay characteristic of the critical path under certain operating conditions 1 is indicated by the line A in FIG. 13, while the power source voltage-delay characteristic of the replica circuit for monitoring the delay time of the critical path is indicated by the line C. In a cycle T under the operating conditions, there is a difference of operating voltages between the critical path and the replica circuit of exactly xcex94V. On the other hand, the power source voltage-delay characteristic of the critical path under certain operating conditions 2 is indicated by the line B in FIG. 13, while the power source voltage-delay characteristic of the replica circuit for monitoring the delay time of the critical path is indicated by the line D. In a cycle T under the operating conditions, there is a difference of operating voltages between the critical path and the replica circuit of exactly xcex94Vxe2x80x2. Such a difference in delay characteristics is caused for example by variability in the current capacity of transistors arising in the production process. In FIG. 13, xcex94V is larger than xcex94Vxe2x80x2 (xcex94V greater than xcex94Vxe2x80x2).
When, for example, a giving a power source voltage margin of exactly xcex94Vxe2x80x2 from the delay information of the replica circuit under the above conditions 2 to an LSI having such characteristics, under the operating conditions 1 of the LSI, the power source voltage becomes insufficient by exactly (xcex94Vxe2x88x92xcex94Vxe2x80x2) and the delay time increases and may lead to operating errors. Thus, in the case of such circuit characteristics, a margin of xcex94V has to be added when controlling the power source voltage considering the operating conditions 1.
However, this margin is excessive in the case of the operating conditions 2. The power source voltage adjusted exactly by the margin becomes higher than the minimum voltage for maintaining normal operation of the LSI and results in wasteful power consumption.
Furthermore, the delay characteristics of the LSI, that is, the relationship between the power source voltage supplied and the delay time, changes in accordance with conditions of producing the LSI. A delay of an LSI is determined by the sum of a gate delay and an RC interconnection delay. Among these, the gate delay is determined by the value of a load capacitance to be driven divided by a current value of the transistor. Since the current capacity of a transistor depending on the power source voltage supplied, the gate delay changes in accordance with the power source voltage. On the other hand, the RC interconnection delay is constant regardless of the operating voltage when the current capacity of the buffer to be driven is large. For example, it is generally known that the time to shift to a power source voltage VDD level can be approximated as (0.38xc3x97Rxc3x97C).
In production of an actual LSI, there are manufacturing variability in the interconnection resistance and interconnection capacitance relating to the RC components and manufacturing variability in the current carrying capacity of transistors relating to the gate delay of the transistors. FIG. 14 is graph of the delay characteristic of a LSI, that is, the relationship of the power source voltage and the delay value. In FIG. 14, the line A indicates the characteristic of an LSI when it ends up as designed, the line B indicates the characteristic of an LSI when the current capacity of the transistor is lower than a design value and an interconnection resistance and interconnection capacitance end up as designed, the line C indicates the characteristic of an LSI when the current capacity of the transistor ends up as designed and the interconnection resistance and interconnection capacitance end up larger than the design values, the line D is an interconnection delay value when an interconnection delay is given as designed, and the line E is an interconnection delay value when a larger interconnection delay than a design value is given. Namely, the component of the line D is included as an interconnection delay value in the line A and line B, and the component of the line E is included as an interconnection delay value in the line C.
As shown in FIG. 14, when there are several patterns of the operating voltage and delay time, the extent of the effect of a change in the operating voltage on the delay value becomes irregular, so it is difficult to determine how much the voltage has to be changed. Particularly, if the voltage is lowered assuming the characteristic of the line C, when the characteristic of the actual LSI is that of the line B, the amount of variability of the delay becomes large, a delay value not satisfying the operating frequency specification is given, and operating error may occur.
The present invention was made in consideration with the above circumstances and has as an object thereof to provide a voltage supply circuit capable of dealing with an abrupt change of a load and supplying a stable operating power source voltage by controlling an amount of increase and amount of reduction of an output voltage of a voltage generation circuit to be mutually different, capable of attaining a lower power consumption by deducing operating conditions of an LSI from delay information detected by a replica circuit and suitably correcting an operating voltage margin, and capable of realizing lower power consumption by deducing operating conditions of the LSI by further detecting an amount of change of the delay information while maintaining normal operation of a semiconductor integrated circuit and a method of controlling the voltage.
To attain the above object, a voltage supply circuit according to a first aspect of the present invention comprises a functional circuit for performing predetermined processing in accordance with an input signal at an operating speed based on a power source voltage supplied and outputting a processing result after a predetermined delay time from when said input signal is received, a delay detection circuit for detecting a delay time of said functional circuit, a control circuit for outputting a control signal to control said power source voltage to raise or lower it in accordance with a delay time detected by said delay detection circuit and to make an amount of change at the time of raising said power source voltage larger than an amount of change at the time of lowering it, and a voltage generation circuit for generating a voltage in accordance with said control signal and supplying it as said power source voltage to said functional circuit.
Also, in the present invention, preferably said delay detection circuit comprises a replica circuit having about the same delay time as that of a critical path of said functional circuit and a delay time detection circuit for inputting a predetermined signal to said replica circuit and detecting a delay time of an output signal corresponding to the input signal.
Also, in the present invention, preferably said control circuit comprises a comparison circuit for comparing a delay time detected by said delay time detection circuit with a reference value set in advance and outputs a control signal to raise the output voltage of said voltage generation circuit by a first amount of change when the result of said comparison is that said detected delay time is larger than said reference value and to lower the output voltage of said voltage generation circuit by a second amount of change smaller than said first amount of change when the result is that said detected delay time is smaller than said reference value.
Alternatively, in the present invention, preferably said control circuit comprises a means for finding a difference of a delay time detected by said delay time detection circuit and a reference value set in advance and a voltage change determining means for setting said amount of change of voltage in accordance with said difference of the delay time and the reference value.
A voltage supply circuit according to a second aspect of the present invention comprises a functional circuit for performing predetermined processing in accordance with an input signal at an operating speed based on a power source voltage supplied and outputting a processing result after a predetermined delay time from when said input signal is received, a replica circuit having almost the same delay time as that of a critical path of said functional circuit, a delay detection circuit for detecting a delay time of said replica circuit, a control circuit for finding a power source voltage by which a delay time of the replica circuit satisfies a predetermined reference value in accordance with a delay time detected by said delay detection circuit, finding a power source voltage to be supplied to said functional circuit based on a relationship of a power source voltage of said replica circuit and a power source voltage of said functional circuit under the same operating conditions, and outputting a control signal in accordance with the power source voltage, and a voltage generation circuit for generating a voltage in accordance with said control signal and supplying it as said power source voltage to said functional circuit.
Also, the present invention preferably comprises a database indicating a relationship of said replica circuit and a power source voltage supplied to said functional circuit so that a delay time of said replica circuit and a delay time of the critical path of said functional circuit becomes equal under the same operating conditions, and said control circuit finds a voltage for supplying to said functional circuit corresponding to said found voltage for supplying to said replica circuit based on said database.
Also, the present invention preferably comprises a formula indicating a relationship of said replica circuit and a power source voltage supplied to said functional circuit so that a delay time of said replica circuit and a delay time of the critical path of said functional circuit becomes equal under the same operating conditions, and said control circuit finds a voltage for supplying to said functional circuit corresponding to said found voltage for supplying to said replica circuit based on said formula.
Furthermore, a voltage supply circuit according to a third aspect of the present invention comprises a functional circuit for performing predetermined processing in accordance with an input signal at an operating speed based on a power source voltage supplied and outputting a processing result after a predetermined delay time from when said input signal is received, a delay detection circuit for detecting a delay time of said functional circuit, a control circuit for obtaining an amount of change of a delay time corresponding to an amount of change of said power source voltage in accordance with a delay time detected by said delay detection circuit, deducing production conditions based on information regarding a power source voltage and a delay time under different production conditions found in advance, finding a power source voltage to be supplied to said functional circuit under the deduced production conditions, and outputting a control signal in accordance with the power source voltage, and a voltage generation circuit for generating a voltage in accordance with said control signal and supplying it as said power source voltage to said functional circuit.
Also, the present invention preferably comprises a database indicating a relationship of said power source voltage and delay time under different operating conditions, and said control circuit deduces production conditions based on an amount of change of said found power source voltage and an amount of change of said delay time and said database and finds a power source voltage by which said functional circuit normally operates under the production conditions based on said database in accordance with said deduced production conditions.
Also, in the present invention, preferably said control circuit comprises a first storage means for storing a delay time detected at a previous time and a set power source voltage and a second storage means for storing a delay time detected at a current time and a set power source voltage and calculates an amount of change of said power source voltage and an amount of change of a delay time in accordance therewith in accordance with data stored in said first and second storage means.
Also, the present invention preferably comprises a replica circuit based on the critical path of said functional circuit, and said delay detection circuit detects a delay time of said replica circuit.
Also, a voltage control method according to a first aspect of the present invention is a voltage control method for supplying a minimum power source voltage by which a functional circuit for performing a predetermined function normally operates, including the steps of detecting a delay time of said functional circuit, raising or lowering said power source voltage in accordance with said detected delay time, setting an amount of change at the time of raising said power source voltage larger than an amount of change at the time of lowering it, and changing said power source voltage in accordance with said set amount of change and supplying it to said functional circuit.
Also, a voltage control method according to a second aspect of the present invention is a voltage control method for supplying a minimum power source voltage by which a functional circuit for performing a predetermined function normally operates, including the steps of detecting a delay time of a replica circuit for monitoring a delay time of said functional circuit, finding a power source voltage by which a delay time of the replica circuit satisfies a predetermined reference value in accordance with a detected delay time of said replica circuit, finding a power source voltage to be supplied to said functional circuit corresponding to said found power source voltage of the replica circuit based on a relationship of a power source voltage supplied to said replica circuit and a power source voltage supplied to said functional circuit under the same operating conditions, and generating said found power source voltage to be supplied to the functional circuit and supplying it to said functional circuit.
Also, a voltage control method according to a third aspect of the present invention is a voltage control method for supplying a minimum power source voltage by which a functional circuit for performing a predetermined function operates normally, including the steps of detecting a delay time of said functional circuit, obtaining an amount of change of a power source voltage supplied to the functional circuit and an amount of change of a delay time corresponding to the amount of change of the power source voltage in accordance with said detected delay time of the functional circuit, deducing production conditions based on said amount of change of the power source voltage and an amount of change of a delay time and a relation between the power source voltage and the delay time obtained in advance, finding a power source voltage to be supplied to said functional circuit under the deduced production conditions, and generating said power source voltage to be supplied and supplying it to said functional circuit.
According to the present invention, a replica circuit having almost the same delay time as that of the critical path of a functional circuit is provided corresponding to the functional circuit for performing predetermined processing in accordance with an input signal, and the functional circuit and the replica circuit are supplied with a power source voltage generated by a voltage generation circuit. The delay time at the time a predetermined input signal is input to the replica circuit is detected by the delay detection circuit, and a control circuit controls the power source voltage supplied to raise or lower it in accordance with a result of comparing the detected delay time and a predetermined reference value. Furthermore, by setting an amount of change of voltage at the time of raising the power source voltage larger than an amount of change of voltage at the time of lowering it, when the power source voltage falls due to a change of the load etc. and the delay time of the critical path of the functional circuit exceeds the predetermined reference value, the power source voltage can be restored to the reference value or more in a short time, the probability of occurrence of operating error in the functional circuit can be kept low, and instability of voltage control can be eliminated by gradually lowering the voltage level by small amounts at the time of lowering the power source voltage.
Also, according to the present invention, when the delay times of the replica circuit and the functional circuit, that is, the critical path of the LSI, differ under the same operating conditions due to variability of semiconductor elements etc., the relationship of an operating power source voltage of the replica circuit and an operating power source voltage of the LSI under different operating conditions are found in advance, the power source voltage supplied to the replica circuit is found in accordance with the delay time of the replica circuit detected during circuit operation, and the power source voltage supplied to the LSI is found based on the relationship of the operating power source voltage of the replica circuit and the operating power source voltage of the LSI found in advance. As a result, an error of the deduced operating power source voltage due to variability of the delay times of the replica circuit and the functional circuit can be corrected, a minimum power source voltage required for normally operating the LSI can be supplied, and a lower power consumption can be realized.
Furthermore, according to the present invention, when the delay characteristics of the functional circuit, that is, the LSI, change due to variability of production conditions etc., the amount of change of the power source voltage supplied to the LSI and the amount of change of the delay time in accordance therewith are detected, a database indicating the relationship of the power source voltage and delay time of the LSI under different production conditions is found in advance, an amount of change of the power source voltage supplied and an amount of change of the delay time can be found in accordance with the delay time of the LSI detected during circuit operation, the production conditions of the LSI can be deduced by referring to the database, and a power source voltage to be supplied to the LSI can be found based on the deduced production conditions.
As a result, estimation error of a power source voltage due to variability of production conditions of the LSI can be corrected, a minimum power source voltage required for operating the LSI normally can be supplied, and a lower power consumption can be realized.